Tone keyer



Patented June 10, 1952 2,599,675 rom KEYER Philip E. V 012,- Elorham Park, N. J., asslgnor to .Radio Corporation of America, a corporation of. Delaware This invention relates to tone 1 keyers or modulators.

Atone keyer is a device by means of which .a carrier wave of tone frequency is keyed (modulated) in accordance with "an intelligence wave. In any modulation system such as this, the keylng frequency will tend to appear in the output, as "well as the tone carrier and sideband frequencies. A desirable characteristic of such a device is "the suppression or elimination of the keying frequency itself in them'odulated output. If the keying frequency is -'elimlnated,rthen the output consists only of the carrier frequency (tone) and its associated intelligence sidebands. When the intelligence consists of on-cit telegraph signals (square wave keying) the linearity of the tone keyer becomes unimportant, since then it is desired to pro'ciuc'eonly 100 modulation (maximum carrier amplitude for mark "and zero carrier amplitude for space).

Byway of example, several rather well-known circuits operate as tone keyers. First may be mentioned the single-ended amplifier. in which either the grid bias or the plate voltage is keyed. This arrangement, however, requires a high pass filter in its output, in order to suppressthe keying transients. Moreover, it'willgive reasonable suppression of keying transients only if the oarrier frequency (tone) is several times the maxl mum intelligence frequency. 3

Another typeis the balanced -modulator, h cancels the keying transients by adding them in phase opposition in the output. However, this requires the use of center tapped transformers havingl'accuratelybalancediwindings.

The ring .modulatoralsoxrequires then-use of center tapped transformers.

Anqobjectof thisinventionis to provide a tone keyer which is considerablyusimpler thanprior circuits.

An additional object is to deviseia, tone keyer which effectively suppresses keying transients Without theuse of filters.

Anotherobjeotis to provide atonekeyer which requires no transformers, although these a .may .be used if desired Ion-D. C. isolation. However, such transformers, if used, can be relatively simple and do notneed tobe center tapped transformers having accurately balanced windings.

A further object is to devise a tone lseyer of novel type which may be used with sin l ended input andoutput.

.Yet another object is to devise atone keyer circuit which requires no balancing of tubes or circuitelements. i

2 Still another object is to i provide a tonefkeyer which requires he source of-" D. C. po\ver,si1ch as'a D. 'C.Ianodesu pply. The foregoing and other 1 objects 'of ithe llnvention will be best understood :from :theefollowihg description of some eitemp'liflc'aton's thereof, referencesbeing had to the accompanying drawlngs, =wh'erem:

Fig. 1 is e. "diagrammatic representation of 57a basic tone ikeyer circuit aaccordin'g 1:01 this invention; Fig. .2 is :aset of curves 111561111111 explaining-the operation :of thisinvention;

1 Fig- 3 its a .modified circuitarrangement; and Fig. 54 'is an arrangement similar to :Eig.f3":biit somewhatmodified.

The objects of this invention are'eccomplished, briefly, in the following manner: a ipair o'f triode structures are connected in parallel with each other and this parallel combination iseonnected in series-between a source of tone input ire;- quency and "a load. resistor; thef'two structures are connected in reverse directions between the source (and the load resistor. .The keying voltage is applied ccphas'ally to the control gridsrcf the two triodes, key'e'd tone f output ibeing. taken from the load resistor. Ina modification, the load resistor .is replaced by the primary winding oisan output. transformer. In :a further mourfication, tone Voltage degrees 'o-ut .ofiphase with the voltage being keyed-isiecl to the triode output, to neutralize tonetfed through the triode's during spacing intervals.

Referring to thedrawings,:Fig.. i isadia'gram of a basic ibone' :keyer circuit according t'o' this invention. rinpiitresistor l :is 'connected across a *pair of toneinput terminals 2 enditerminal 3 :being grounded as shown. Terminals 2 sand-3 are connected to a suitable sour ce cnotshown) of voltage of tone frequency, "for "example; ten kilocycles. The, toneinput may File-substantially sinusoidal, asshown inFig. -2,':line b. An output or load resistor! is connected eacrossfiazpair 0f keyed tone output terminals sland. 6,.terminelt being groundedas shown. Thus, theptoneslnput d e ed tone output aven-common ounde terminal. Keyed tone appears across resistorl. as. will be, described, and terminalsjli andyfi :may' be connected toany suitable load devicessuch as a line. for conveying the keyed tone-15o; a distant point.

Two triode. vacuum tube-electrode structures and 8 are connectedtin.paralleland.thesparallelcombinationis connected .in series ybetw een th hishwt ntm input t rm n I! n th @h-Is'h potential output terminal 5. Although these vacuum tube structures are shown in separate envelopes, it will be appreciated that they can both be positioned within a single envelope, and to effect this purpose a tube of the twin-triode type, such as type GSN'Z-GT, could be used for structures 1 and 8. The anode-cathode paths of structures 1 and 8 are connected reversely between input resistor and output resistor 4. The anode 9 of structure I and the cathode ill of structure 8 are both connected to terminal 2, while the cathode ll of structure 7 and the anode l2 of structure 8 are both connected to terminals.

The control grids of structures 'i and 8 are con- 1 nected together and through a resistor l3 to one terminal is of a pair of keying input terminals l4 and I5, terminal it being grounded. Thus, in Fig. 1, tone input terminal 3, keying input terminal l5 and output terminal 6 are all common and grounded. -Terminals it and 55 are connected to be supplied with pulsating direct current energy from a suitable source (not shown), the amplitude of this pulse energy changing between a first value respresenting mark and a second value representing space. This change may, for example, be at a rate of 171 cycles per second. As an example, the keying voltage may be as represented in Fig. 2, line a, a substantially square wave with the positive excursions corresponding to mark and the negative excursions to space. For example, the keying input terminals l4 and I5 may be connected to the output of a diversity receiver of the type described in School: et a1. Patent #2515568, dated July 18, 1950. The output of such receiver may have the wave form illustrated in Fig. 2, line a.

. Assume a sine wave tone input across resistor I, as shown in Fig. 2, line b. The keying input voltage at terminal [4 for space interval, as shown at d in Fig. 2, line a, is made sufficiently negative to block or cut off triodes l and 8 throughout the entire cycle of tone input. The keyed tone output is shown in Fig. 2, line 0. During space, both tubes 'i' and 8 are cut off, so that the output is zero during this interval, as illustrated at e in Fig. 2, line 0.

For mark interval, the keying input voltage at terminal It, as shown at i in Fig. 2, line a, is made more positive than the positive peak of the tone input cycles of Fig. 2, line b. During a negative half cycle of tone input, structure I is blocked or nonconducting, since its anode 9 is then negative with respectto its cathode ll. Structure 8 conducts during this negative half cycle of tone input since its anode i2 is then positive with respect to its cathode ID. This will provide output at resistor 4. During this time of conduction triode 8 acts like a constant resistance because its grid-cathode voltage is essentially fixed due to the clamping action of a grid supply voltage 1 which is greater than the tone voltage applied to cathode Ill, and also due to the series grid resistor l3. For all practical purposes the gridcathode voltage of 8 is zero during this period. During the negative half cycles of tone input voltage occurring during mark intervals, structure 8 conducts and operates along its diode line. Then the keyed tone output voltage across resistor 4 is equal to the tone input voltage minus the diode drop in 8.

During a positive half cycle of tone input, structure 8 is blocked or nonconducting, due to anegative anode-to-cathode voltage. Structure 1 conducts during this positive half cycle of tone 4 input since its anode 9 is then positive with respect to its cathode II. This will provide output at resistor l. During this time of conduction the grid of 1 remains clamped at cathode I I. In order for the grid of i to remain clamped, the keying input voltage must be more positive than the cathode I i can ever be. The maximum positive voltage that can appear at the cathode II is the positive peak value of the input tone, this appearing at cathode II when 1 conducts during positive half cycles of input tone. However, the

- keying input voltage at f is more positive than the positive peak of the tone input cycles, so that the keying input voltage is more positive than the cathode II can ever be. Therefore, during mark periods and during positive half cycles of tone input voltage, 1 conducts and since the keying voltage is more positive than the peak tone input voltage, the grid of l is clamped at (held at essentially the same potential as) cathode ll. Structure i is then operating along its diode line. Then the keyed tone output voltage across resistor 4 is equal to the tone input voltage minus the diode drop in I.

It is important that the grid of whichever triode is conducting be clamped to its cathode. If the grid is clamped to its cathode the triode acts like a fixed resistance. However, if the grid is not clamped to its cathode the triode acts like a variable resistance and the output tone waveshape will be distorted.

The keyed tone output during mark intervals such as of the keying voltage is shown at g in Fig. 2, line 0.

The right hand portion of Fig. 2 illustrates the operation of the circuit with the tone input removed, demonstrating the suppression of the keying frequency. It will be noted in line b of Fig. 2 that the tone input is zero for the right hand portion or" the figure.

During the space interval the keying voltage is negative at d, this negative voltage being applied to the grids of both I and 8. There is no current fiow through the grid circuit of either triode at this time, the grids both being negative with respect to their respective cathodes, which are now substantially at ground or zero potential. Therefore, during space the output voltage is zero, as shown at e.

During the mark interval the keying voltage is positive at i, this positive voltage being applied to the grids of both 7 and 8. The keying voltage input applied to the grid of 1 being more positive than the cathode H, which is now substantially at ground potential, the grid of l clamps at cathode Il, so that current flows through the load resistor 41, the conducting grid resistance of triode 1, and the series resistor l3 and terminal I4 back to ground it. The voltage drop across resistor 4 gives an output voltage during this time, as illustrated at h in Fig. 2. Thus, as illustrated at h and e, an output voltage of the keying frequency will appear across output terminals 5 and 6. However, this output may be made negligible by making resistor 13 very large as compared to resistor d. In a practical circuit according to this invention, 30 to 40 db. suppression of the keying frequency is readily obtained.

Of course, when the positive mark keying voltage is applied to the grid of 8, the grid of 8 clamps at cathode it, since cathode I0 is at ground potential when the tone input is removed. Current flows through the input resistor I, the conducting grid resistance of triode 8 and the series resistor l3 and terminal l4 back to ground I 5. However, this current does not flow through load resistor 4 so cannot appear in the output of the circuit.

If the diode resistance of triodes 7 and 8 is small compared to the load resistance 4, amplitude distortion is negligible and inherent differences between tubes have a negligible effect. If the load impedance 4 is high compared to the tube plate resistance, then if the two tubes have diiferent plate resistances, the percentage difference in the amplitudes of positive and negative half cycles is considerably less than the per centage difference in the plate resistances. Therefore, no balancing of tubes or circuit elements is required. Also, when each tube conducts its grid-cathode voltage is zero, due to the clamping action. This makes the tubes act like fixed resistances.

In addition, the circuit of Fig. 1 requires no transformers and has single-ended input and output, with a common terminal between tone input and keyed tone output. It will be noted that no source of D. C. power is required for the circuit of this invention, thus considerably simplifying said circuit as compared with prior circuits.

A multiple tone keyer can be made by using a multiplicity of tone keyers of the type shown in Fig. 1. The keyers would all have a common load resistor 4, but each would have a separate tone input and keying input. The multiple tone keyer would then supply the aggregate signal output of the multiplex telegraph transmitter, in the form of keyed tones.

If it is not desirable to have a common terminal for tone input and keyed tone output, as shown in Fig. 1, an input transformer and/or an output transformer may replace resistors I and 4. Such a circuit is shown in Fig. 3, to which reference will now be made. In this figure, elements the same as those of Fig. 1 are denoted by the same reference numerals. Tone input terminals 2 and 3' are connected to opposite ends of the primary winding 16 of an input transformer 11 to one end of the secondary [B of which anode SJ and cathode are connected. The other end of winding I8 is connected to one end of the primary winding 19 of an output transformer 20, cathode II and anode [2 being connected to the other end of winding 19. Output terminals and 6' are connected to opposite ends of the secondary 2| of transformer 20. Thus, tone input terminals 2 and 3 and keyed tone output terminals 5 and 6' are entirely separated from each other. Winding [9 has an eifective resistance which is low as compared to grid resistor l3, thus greatly reducing the keying voltage appearing in the output during mark interval, when there is no tone input. This corresponds to the relative values of resistors 4 and I3 in Fig. 1.

The keying input can also be supplied through a transformer, if it is so desired, and this feature is illustrated in Fig. 3. Keying input terminals [4 and I5 are connected, to opposite ends of the primary'winding 22 of a keying transformer 23 to one end of the secondary 24' of which the grids of triodes 1 and 8 are connected, through resistor l3. Since no-D. C. can be coupled through transformer 23, a bias source may be needed for the grids of triodes l and 8. For this-purpose, a biasing battery 25, poled asshown, may be connected between the remaining end of secondary winding 2.4 and one endof winding 18, to prol hiasand 1 QWPWQQ th k i g? in ut Qi fiil ix b iii to triodes 7 and 8. However, transformer icon-.- pling of a D. C. telegraph signal, :as shown in Fig. 3, may not be .verypractical.

It will be noted that the D. C. source 2.5 is needed only for bias purposes. In Fig. 3, as .in Fig. 1, no D. C. anode voltage is applied .togthe keyer triodes l and .8; only itone signal is applied as anode voltage.

The operation of the circuit of Fig. 3 is ex.- actly the same as that of Fig. 1, previously ,described, so it will not be repeated here.

Reference will now be made to Fig. f1, which shows a modified tone keyer circuit capable ,of being used in an electronic multiplex ;telegraph transmitter of the type shown in -,the,co pending Shenk etal. application, fierial No. 21 1,272 i'1led February '16, 1951. The ,circuit of Fig. 4 re.- sembles that of Fig. 3, and elements the same as those of Fig. 3 are denoted by thesamereference numerals. In Fig. 4, the entire circuit operates at a potential such as volts hove ground, and the keying input voltage is volts for mark and +15. volts for space, as in:- dicated. The keying input is fed thrqu h :9 re.-

sistor 13 to the grids of the two triodes 1 and 8,,asin'Fig. 1.

In Fig. 4, the potential level for the entire circuit is established by connecting a point .26 to. the center tap of input secondary I8 and to the end of output winding 'l B which is opposite to the end to which cathode H and anode l2 are connected. Point 26 is the junction between two series-connected voltage dividing resistors 21 and 28 which are connected between a positive po.- tential source of volts and ground. Resistor 2B is bypassed by capacitor 29.

By analogy to Fig. 3, it may be seen that the tone voltage being keyed is provided between the center tap of winding 18 and the .upper end of said winding. In the electronic multiplex transmitter of said copending application, it wasrequired to key tones of frequencies up to 8 kc. At these frequencies the feed through of tone, from input to output, during spacing intervals, due to interelectrode capacitances in triodes 1 and 8, was more than could be tolerated. For this reasoma center tapped input transformer 11 is used to obtain a source of voltage out of phase with that being keyed, to allow neutralizing of this feed through. Such an out-of-phase volt ge 31 pears at the lower end of winding I8. This cut.- of-phase voltage fed through a capacitor .30 which is connected between the lower end of winding is and the common junction of cathode properly related values may be employed.

Resistor l3 megohins- 2.2 Resistor Z1 ohms 150,000 Resistor 28 do 130,000 Capacitor 29 mfd 0.1 Capacitor 30 mmfd i 7.5 Triode l 6SN7-GT Triode 8 do What Iclaim to. be .myinventionuis as-followsiz M ns ls v si ianommu e nnermost terminals and tone output terminals, a pair'of parallel-connected controllable unidirectional electron flow devices connected between the input terminals and the output terminals, said pair of devices being connected to conduct in opposite directions and each having a control electrode for control of the electron flow in the respective device, and means for applying a keying voltage to the control electrodes of said devices to control the electron flow therein.

2. A tone keyer circuit, comprising a pair of oppositely-arranged parallel-connected controllable electron flow devices each having a control electrode, means for applying tone input voltage to said devices, an output circuit connected to said devices, and means for applying a keying voltage to the control electrodes of said devices to control the electron flow therein.

3. A tone keyer circuit, comprising a pair of electron flow devices each having at least an electron-emitting electrode, an electron-receiving electrode and a control electrode, means for applying tone input voltage to the electron-receiving electrode of one device and to the electronemitting electrode of the other device, an output impedance connected to the electron-emitting electrode of said one device and to the electronreceiving electrode of said other device, and means for applying a keying voltage cophasally to the control electrodes of both devices to control the electron flow therein.

4.-A tone keyer circuit, comprising a pair of tone input terminals and a pair of tone output terminals, a pair of parallel-connected controllable unidirectional electron flow devices connected between one of the input terminals and one of the output terminals, said pair of devices being connected to conduct in opposite directions and each having a control electrode for control of the electron flow in the respective device, means connecting the remaining input terminal and the remaining output terminal both to a point of fixed reference potential, and means for applying a keying voltage to the control electrodes of said devices to control the electron flow therein. a

5. A tone keyer circuit, comprising a pair of tone input terminals and a pair of tone output terminals, a pair of electron flow devices each having at least an electron-emitting electrode, an electron-receiving electrode and a control electrode, means connecting the electron-receiving electrode of one device and the electron-emitting electrode of the other device to one input ter-- minaljmeans connecting the electron-emitting electrode of said one device and the electron-receiving electrode of said other device to one output terminal, means connecting the remaining input terminal and the remaining output terminal both to a point of fixed reference potential, and means for applying a keying voltage cophasally to the control electrodes of both devices to control the electron flow therein.

7 6. A tone keyer circuit, comprising a pair of tone input terminals and a pair of tone output terminals, means connecting said input terminals to the primary winding of an input transformer, means connecting said output terminals to the secondary winding of an output transformer, a pair of parallel-connected controllable unidirectional electron flow devices connected between one end of the secondary winding of said input transformer and one end of the primary winding of said output transformer, said pair of devices being connected to conduct in opposite directions, means connecting a spaced point on the secondary winding ofsaid input transformer to the remaining end of the primary winding of said output transformer, and means for applying a keying voltage to said devices to control the electron fiow therein.

'7. A tone keyer circuit in accordance with claim 6, wherein said spaced point is the remaining end of the input transformer secondary Winding.

8. A tone keyer circuit in accordance with claim 6, wherein said spaced point is an intermediate point on the input transformer secondary winding.

9. A tone keyer circuit in accordance with claim 6, wherein said spaced point is an intermediate point on the input transformer secondary winding and wherein the remaining end thereof is coupled to said one end of the output transformer primary winding. 4

10. A tone keyer circuit in accordance with claim 6, wherein said spaced point is an intermediate point on the input transformer secondary winding and wherein the remaining end thereof is coupled through a capacitor to said one end of the output transformer primary winding.

11. A tone keyer circuit, comprising a pair of tone input terminals and a pair of tone output terminals, means connecting said input terminals to the primary winding of an input transformer, means connecting said output terminals to the secondary winding of an output transformer, a pair of controllable electron flow devices each having at least an electron-emitting electrode and an electron-receiving electrode, means connecting the electron-receiving electrode of one device and the electron-emitting electrode of the other device to one end of the secondary winding of said input transformer, means connecting the electron-emitting electrode of said one device and the electron-receiving electrode of said other device to one end of the primary winding of said output transformer, means connecting a spaced point on the secondary winding of said input transformer to the remaining end of the primary winding of said output transformer, and means for applying a keying voltage to said devices to,

control the electron flow therein.

tone input terminals and a pair of tone output terminals, means connecting said input terminals to the primary winding of an input transformer, means connecting said output terminals to. the secondary winding of an output transformer, a pair of electron flow devices each having at least an electron-emitting electrode, an electron-receiving electrode and a control electrode, means connecting the electron-receiving electrode of one device and the electron-emitting electrode of the other device to one end of the secondary winding of said input transformer, means connecting the electron-emitting electrode of said one device and the electron-receiving electrode of said other device to one end of the primary winding of said output transformer, means connecting a spaced point on the secondary winding of said input transformer to the remaining end'of the primary winding of said output transformer,

and means for applying a keying voltage cophasally to the control electrodes of both devices claim 12, wherein said spaced point is an inter mediate point on the input transformer secondary winding.

15. A tone keyer circuit in accordance with claim 12, wherein said spaced point is an intermediate point on the input transformer secondary winding and wherein the remaining end thereof is 'c'oupled to said one end of the output transformer primary winding.

PHILIP E. VOLZ.

REFERENCES CITED The foilowin references are of record in the file of this patent:

1 UNITED STATES PATENTS Number Name Date 2,335,265 Dodington Nov. '30, 1943 2,460,061 Chapin Jan. 25, 1949 OTHER REFERENCES 

